The present invention relates to an improved method for repairing asphalt pavement roads containing utility cut trenches, potholes, and other discontinuities.
Utility companies must frequently cut trenches into roads and sidewalks in order to place new utility lines or to repair existing defective utility lines. Such openings are commonly designated as "utility cuts." After placement or repair of utility lines, the trench must be backfilled with a material which will ultimately support a patch in the overlying pavement. Similarly, potholes and other discontinuities in roads and sidewalks require repair, sometimes frequently. Repair and maintenance of utility cuts, potholes, and other pavement discontinuities drain resources away from the responsible governmental authority and ultimately from taxpayers.
When utility cuts are repaired, a "temporary patch" is generally placed over the backfilled trench. Commonly used backfills include the subbase materials excavated from the trench, light strength concrete, manufactured and natural gravel, soil cements, and the like. In prior art repair methods, gravel backfill must be compacted and soil cements must "set", i.e. consolidate or settle, prior to placement of the temporary patch. The underlying ground layer is allowed to consolidate or settle for a period of time, which may vary from about thirty days to about a year. All backfill materials may consolidate and/or settle over time. The temporary patch is then excavated, using a jackhammer, saw, or the like, and any surface irregularities, such as those resulting from settlement and/or consolidation which has occurred are corrected. The temporary patch is then replaced by a permanent patch.
An improved method of patching asphalt pavement, useful only when compacted soil cement is the backfill material (the PatchMaster.TM. method), eliminates the need to excavate the temporary patch by setting the surface of the soil cement with heat, scarifying the surrounding patch and bonding additional (single gradation) asphalt concrete to the heated area. However, the PatchMaster.TM. method is limited in its utility. The amount of time required to set soil cement backfill by heat limits the size and number of utility cuts which can be repaired using known Mating equipment. Most bituminous concrete pavements are formed of base and top layers having separate and distinct gradations of bituminous concrete for each layer. The PatchMaster.TM. method does not restore the original structure of such asphalt pavements, i.e., the separate base and top layers. Moreover, the PatchMaster.TM. method does not compensate for consolidation and/or movement of the backfill and surrounding subbase formed by the earth or ground underlying the patch, which occurs as a normal result of thermal expansion and contraction, of shrinkage of the soil cement backfill, or of traffic on the pavement.
Conventional temporary patches are installed directly over the backfilled trench. This practice is not substantially changed by the PatchMaster.TM. method. Consequently, the boundary of the patch substantially overlies the boundary of the trench and the patch has no contact with the undisturbed solid ground surrounding the excavated area. In such instances, the patching materials used in the patch bonds with the vertical edge of the existing asphalt pavement where the patch boundary and existing pavement interface, by virtue of the nature of asphaltic materials. In the PatchMaster.TM. method the existing vertical edge is merely heated and loosened. At a later date, the temporary patch may (or may not)be excavated and replaced with a permanent repair sometimes enlarging the interfacing area, occurring around the original perimeter of the temporary patch. When the temporary patch is not excavated, the interfacing area remains relatively small, occupying substantially the area over the original trench, representing an inherent structural weakness. Even when the gravel backfills are compacted, and/or soil cements are set, the possibility of further consolidation of the ground underlying the permanent patch remains, since it is not possible to compensate completely for the differential of movement in the backfilled area as opposed to the surrounding subbase or subgrade, resulting from the initial disturbance by excavation of the utility cut. The lack of contact between the patch and solid ground in such circumstances creates inherent weakness that is amplified by the use of single gradation bituminous concrete in conventional temporary and sometimes in permanent patches.
The need remains, therefore, for improved temporary and/or permanent repair methods for asphaltic pavement which has been subjected to utility cuts or which contains potholes or other discontinuities.
It is an object of the present invention to provide an improved method and apparatus for effecting repair of utility cuts, potholes, and the like in asphaltic pavement.